Compressor Unit

Abstract

To prevent elimination of liquefaction of oxygen which is a combustion supporting gas and secure maintainability easily in a reciprocation compressor.SOLUTION: A compressor unit 10 includes a compression stage 12 which compresses hydrogen gas which is a boil-off gas from a liquid hydrogen tank. The compression stage 12 includes: a cylinder part 31; a piston 32; a piston rod 33 which connects the piston 32 with a crank mechanism 14; a cover part 25 disposed at the outer side of the cylinder part 31; a nitrogen gas supply part 46 which supplies nitrogen gas to a heat insulation space 28 between the cover part 25 and the cylinder part 31; and a control unit 50 which controls the nitrogen gas supply part 46 so that nitrogen gas is supplied to the heat insulation space 28 when the compression stage 12 compresses the hydrogen gas.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a reciprocating compressor unit. [Background technology]

[0002] In recent years, with environmental considerations in mind, hydrogen has been considered for use as a fuel for power generation and automobiles, and the demand for hydrogen is increasing. Conventionally, low-temperature boil-off gas (BOG) from liquefied natural gas (LNG) and liquid hydrogen (LH2) is recovered using a compressor and supplied to users such as drive systems and power generation facilities. The boil-off gas generated from LH2, in particular, is extremely low in temperature. Therefore, if a compressor is designed to directly draw in the boil-off gas, it is necessary to select materials suitable for extremely low temperatures, adopt design conditions that take into account the amount of thermal deformation, and implement strict insulation treatment, among other constraints. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-172870 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, Patent Document 1 points out the following problem: "In recent years, hydrogen has been attracting attention as a new energy source. When using hydrogen as an energy source, it is expected that it will be stored and transported in a liquefied state, like natural gas. However, hydrogen has the characteristic that its liquefaction temperature is lower than that of air. Therefore, if equipment such as reciprocating compressors designed for natural gas, etc., is applied to hydrogen as is, there is a possibility that problems will occur due to the cryogenic liquid hydrogen. For example, liquefied air will be generated around the equipment that supplies liquid hydrogen and its boil-off gas."

[0005] Therefore, the issue of preventing problems caused by cryogenic liquid hydrogen is being studied. Specifically, a vessel is formed around the compression section to form a vacuum region. However, to maintain the vacuum state, the vessel requires sealing means, such as a lid for internal inspection and the connection with the section where gas flows in and out of the compression section. Furthermore, because the inside of the vessel is in a vacuum state, strength (plate thickness) and reinforcement are required to withstand the pressure difference between the external pressure (atmospheric pressure) and the internal pressure. This compromises maintainability. In addition, various measures are required, such as providing a base inside to support the cylinder.

[0006] Therefore, the present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to prevent liquefaction of oxygen, which is one of the main components of air and also a combustion-supporting gas, and to make it easier to maintain a reciprocating compressor. [Means for solving the problem]

[0007] The compressor unit according to the present invention is a reciprocating compressor unit that recovers hydrogen gas, which is boil-off gas, from a liquid hydrogen storage tank and supplies at least a portion of the recovered hydrogen gas to a demand destination including at least one of an engine, a power generation facility, and a boiler, and includes a compression stage that compresses the hydrogen gas that flows out of the liquid hydrogen storage tank and flows through an intake passage, and a crank mechanism that drives the compression stage. The compression stage includes a cylinder portion, a piston, a cover portion that is disposed outside the cylinder portion, a nitrogen gas supply portion that supplies nitrogen gas to a heat insulating space between the cover portion and the cylinder portion, and While the compression stage is compressing the hydrogen gas, and a nitrogen gas discharge unit that discharges nitrogen gas from the heat insulation space. The compressor unit further includes a control unit that controls the nitrogen gas supply unit so that nitrogen gas is supplied into the heat insulation space while the compression stage is compressing the hydrogen gas.

[0008] In the compressor unit according to the present invention, the oxygen concentration in the air in the heat-insulating space can be reduced as much as possible by filling the heat-insulating space between the cover and the cylinder with nitrogen gas, which prevents the air (outside air) around the cylinder from being cooled by the boil-off gas (intake gas) of liquefied hydrogen, a low-temperature gas, and thereby prevents the liquefaction of oxygen, a combustion-supporting gas.

[0009] Furthermore, maintainability is improved compared to compressors such as those disclosed in Patent Document 1, which require connecting a vacuum pump or the like to the space between the cylinder and the container to create a vacuum every time a portion of the container is opened to inspect or maintain the cylinder. In other words, since there is no need to create a vacuum in the insulation space, there is no need to install equipment to create a vacuum in the insulation space.

[0010] The compressor unit may further include a pressure equalization means for making the pressure inside the heat insulating space approximately equal to atmospheric pressure.

[0011] In this embodiment, the heat insulating space is always at approximately atmospheric pressure. Therefore, there is no need to use a plate material with a thickness required to withstand the differential pressure as the cover. Furthermore, there is no need to provide a large number of bolts in the openings in the cover to contain the pressure. Furthermore, since no sealing function is required, weight can be reduced and simplified structures such as bolts and seals can be used. This improves maintainability and makes it easier to accommodate larger sizes.

[0012] The cover portion may be configured by a metallic outer cylindrical member fixed to the cylinder portion so as to maintain the formation of the heat insulating space in a predetermined shape.

[0013] In this aspect, the cover portion is configured by the outer tubular member fixed to the cylinder portion, so that the shape of the heat insulating space is maintained in a predetermined shape.

[0014] The nitrogen gas exhaust section may include an exhaust passage section having an exhaust pipe fixed to the outer tube member so as to open into the insulation space, and an exhaust valve which is a valve arranged on the exhaust pipe.

[0015] In this embodiment, while the compression stage is compressing the hydrogen gas, the nitrogen gas continues to flow through the heat insulating space, so that the nitrogen gas can be prevented from being cooled and liquefied.

[0016] The compressor unit may further include a temperature sensor that detects the temperature of the nitrogen gas in the discharge passage. In this case, the control unit may control the nitrogen gas supply unit to increase the supply amount of nitrogen gas when the temperature detected by the temperature sensor is equal to or lower than a threshold value estimated from the liquefaction temperature of the nitrogen gas.

[0017] In this embodiment, liquefaction of nitrogen gas can be more reliably prevented, and excessive consumption of nitrogen can be suppressed.

[0018] The compressor unit may further include a cotton-like or sponge-like insulating material. In this case, the cover may be formed of a sheet member arranged to cover the insulating material, and nitrogen gas may be supplied into the insulating space inside the sheet member by the nitrogen gas supply unit.

[0019] In this embodiment, unlike in the case where the cover is constituted by an outer cylindrical member fixed to the cylinder, a container-shaped outer cylindrical member that covers the cylinder is not required, which reduces the burden of attachment and detachment work during maintenance, etc., and makes it easier to accommodate larger sizes. In other words, compared to when the cover is constituted by a metal outer cylindrical member, it is possible to reduce the weight of the members that constitute the cover, improving maintainability. Note that, although the inside of the sheet member that covers the heat insulating material functions as a heat insulating space, this heat insulating space is not limited to an enclosed space.

[0020] The cover may be breathable. In this embodiment, nitrogen gas in the heat insulating space can be appropriately discharged to the outside, thereby preventing the sheet member from expanding.

[0021] The compressor unit may further include a temperature sensor for detecting the temperature of the nitrogen gas in the insulation space. In this case, the control unit may control the nitrogen gas supply unit to increase the supply amount of nitrogen gas when the temperature detected by the temperature sensor is equal to or lower than a threshold value estimated from the liquefaction temperature of the nitrogen gas.

[0022] In this embodiment, liquefaction of nitrogen gas can be more reliably prevented, and excessive consumption of nitrogen can be suppressed.

[0023] The compression stage may further include an adapter portion connecting the cylinder portion and a case of the crank mechanism, the adapter portion including at least one partition portion dividing an internal space of the adapter portion into a plurality of spaces. In this case, hydrogen gas may be present in the space closest to the compression chamber, and nitrogen gas may be present in the space closest to the crank mechanism, and the temperature of the hydrogen gas in the space closest to the compression chamber may be higher than the liquefaction temperature of the nitrogen gas in the space closest to the crank mechanism.

[0024] In this embodiment, the adapter section is provided with a partition section, which more reliably prevents contact between the low-temperature boil-off gas (suction gas) and the nitrogen gas. Also, since the temperature of the hydrogen gas in the space on the compression chamber side is higher than the liquefaction temperature of the nitrogen gas in the space on the crank mechanism side, liquefaction of the nitrogen gas can be prevented.

[0025] The compression stage may be a horizontal type in which the piston slides horizontally. In this case, the cylinder portion may include an intake valve located on an upper side in the direction of gravity and an exhaust valve located on a lower side in the direction of gravity.

[0026] If the lower side is the suction side, the support part of the cylinder is located on the suction side, which has a lower temperature, which can lead to increased effects of freezing and thermal contraction around the support part. Furthermore, even if nitrogen liquefies on the outer surface of the cylinder, the liquid will gasify as it flows to the lower, higher-temperature discharge side. In contrast, in a configuration in which the suction valve is located on the upper side in the direction of gravity, as in this embodiment, the support part is located on the higher-temperature discharge side, which can reduce the effects of freezing and thermal contraction. [Effects of the Invention]

[0027] As described above, according to the present invention, it is possible to prevent liquefaction of oxygen, which is one of the main components of air and also a combustion-supporting gas, and to facilitate maintenance of a reciprocating compressor. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is a diagram schematically illustrating a configuration of a compressor unit according to a first embodiment. [Figure 2] FIG. 4 is a diagram schematically illustrating a configuration of a compressor unit according to a modified example of the first embodiment. [Figure 3] FIG. 4 is a diagram schematically illustrating a configuration of a compressor unit according to a modified example of the first embodiment. [Figure 4] FIG. 6 is a diagram schematically illustrating the configuration of a compressor unit according to a second embodiment. [Figure 5] FIG. 10 is a diagram schematically illustrating a configuration of a compressor unit according to a modified example of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0029] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0030] (First embodiment) The compressor unit according to this embodiment is configured to recover hydrogen gas, which is boil-off gas, from a liquid hydrogen storage tank, compress the recovered hydrogen gas, and supply it to a consumer. This allows for efficient supply of hydrogen gas. The boil-off gas, which is hydrogen gas, has a temperature of approximately −253°C. Consumers include at least one of an engine, a power generation facility, and a boiler, but may also include facilities other than those that utilize gas as an energy source, such as gas combustion facilities, flaring facilities, and vents. Furthermore, the hydrogen gas discharged from the compressor unit does not necessarily need to be supplied directly to a consumer. For example, the hydrogen gas may be filled into a cylinder and then supplied to a consumer by various means, such as transporting the cylinder or using gas piping connected to the cylinder.

[0031] 1, the compressor unit 10 includes a compression stage 12 for compressing hydrogen gas and a crank mechanism 14 for driving the compression stage 12. The hydrogen gas compressed in the compression stage 12 is discharged to a discharge flow path 18. The hydrogen gas compressed in the compression stage 12 and flowing through the discharge flow path 18 is supplied to a demand destination not shown.

[0032] A downstream compression stage (not shown) may be provided on the discharge side of the compression stage 12. In this case, the hydrogen gas is compressed in the compression stage 12 and then further compressed in the downstream compression stage, and is sent to a consumer.

[0033] The compression stage 12 is connected to the liquid hydrogen storage tank 23 via the suction passage 21. Therefore, boil-off gas (BOG) of the liquefied gas generated in the liquid hydrogen storage tank 23 is drawn into the compression stage 12 through the suction passage 21. Note that the suction passage 21 does not need to be directly connected to the liquid hydrogen storage tank 23, as long as it allows the boil-off gas generated in the liquid hydrogen storage tank 23 to flow through it.

[0034] The compression stage 12 is configured by a reciprocating compression mechanism. That is, the compression stage 12 includes a cylinder portion 31, a piston 32 arranged in the cylinder portion 31, and a piston rod 33 connected to the piston 32. The piston rod 33 is connected to the crank mechanism 14. The piston 32 reciprocates within the cylinder portion 31, thereby compressing hydrogen gas within a compression chamber 34.

[0035] The compression stage 12 may be of a horizontal type in which the piston 32 slides horizontally. In this case, the suction valve 21a provided in the cylinder portion 31 between the portion where the suction passage 21 is connected and the compression chamber 34 is located on the upper side in the direction of gravity, and the discharge valve 18a provided in the cylinder portion 31 between the portion where the compression chamber 34 is connected and the discharge passage 18 is located on the lower side in the direction of gravity. The compression stage 12 may also be of a vertical type in which the piston 32 slides vertically.

[0036] 1 shows the compression stage 12 having a double-acting structure, but a single-acting structure may also be adopted for the compression stage 12. Furthermore, the compression stage 12 does not necessarily have to be composed of one cylinder, but may be composed of multiple compression stages connected in parallel. In other words, the compression stage 12 may be configured such that hydrogen gas is compressed and pressurized by pistons 32 in multiple cylinder sections 31 connected in parallel.

[0037] A cover portion 25 is disposed on the outside of the cylinder portion 31 so as to form a space between the cover portion 25 and the cylinder portion 31. In this embodiment, the cover portion 25 is configured by an outer tube member 26 that is fixed to the cylinder portion 31 to form a space between the cover portion 25 and the cylinder portion 31.

[0038] The outer cylinder member 26 is made of a material that does not easily deform, such as a metal. When the outer cylinder member 26 is attached to the cylinder portion 31, a space of a predetermined size is formed around the cylinder portion 31. As described below, nitrogen gas is introduced into this space, which functions as an insulating space 28 that eliminates oxygen around the cylinder portion 31 and thermally isolates it from the outside air (atmosphere). In other words, the insulating space 28 is provided around the portion that forms the compression chamber 34, thereby preventing oxygen in the outside air from liquefying around the cylinder portion 31. Because the outer cylinder member 26 is made of a material that does not easily deform, the shape of the insulating space 28 is maintained in a predetermined shape.

[0039] The outer cylinder member 26 is attached, for example, to a rear head 31a that is a part of the cylinder portion 31. However, the outer cylinder member 26 does not need to be fixed to the rear head 31a, and may be attached anywhere in the cylinder portion 31 as long as the heat insulating space 28 can be formed.

[0040] The outer tubular member 26 is provided with an opening through which the piping forming the discharge flow path 18 (piping connected to the cylinder portion 31) passes, as well as an opening through which the piping forming the suction flow path 21 passes. Gaps or holes (hereinafter referred to as "leakage portions 29") are intentionally provided between these piping and the openings. The outer tubular member 26 is also provided with an opening (not shown) through which the support for the cylinder portion 31 passes. Leakage portions 29 are also intentionally provided between the support and the openings. In the compression stage 12, these leakage portions 29, together with the discharge passage portion 48 described below, serve as nitrogen gas discharge portions that discharge the nitrogen gas inside. Note that other leakage portions (not shown) that appropriately discharge the nitrogen gas inside may be added to the outer tubular member 26.

[0041] The compression stage 12 includes a rod packing portion 36 provided in the cylinder portion 31, a hollow adapter portion 37 arranged adjacent to and connected to the cylinder portion 31, and a crankcase 38 that houses a crankshaft, which is part of the crank mechanism 14.

[0042] The adapter part 37 is formed in a cylindrical shape, and the piston rod 33 is disposed in the space inside the adapter part 37. One longitudinal end of the adapter part 37 is connected to the cylinder part 31. The other longitudinal end of the adapter part 37 is connected to the crankcase 38. A partition wall 40 is provided at this other end, separating the internal space of the adapter part 37 from the space inside the crankcase 38.

[0043] The rod packing portion 36 is fixed to the rear head 31a. The rod packing portion 36 is provided to prevent hydrogen gas in the compression chamber 34 from leaking out of the cylinder portion 31 through the gap between the rear head 31a and the piston rod 33.

[0044] The adapter part 37 has a partition part 44 that divides the internal space into a space on the compression chamber 34 side (first space 37a) and a space on the crank mechanism 14 side (second space 37b). The piston rod 33 also passes through this partition part 44. A seal part 44a is provided on the periphery of the through hole in the partition part 44, through which the piston rod 33 passes.

[0045] The compression stage 12 is equipped with a nitrogen gas supply unit 46 that supplies nitrogen gas to the heat insulation space 28. The nitrogen gas supply unit 46 has a supply path 46a fixed to the outer tubular member 26 so as to open into the heat insulation space 28, and a supply valve 46b that is a valve disposed in the supply path 46a. The supply path 46a is connected to a nitrogen gas source 47, and receives a supply of nitrogen gas from the nitrogen gas source 47. The supply valve 46b is configured, for example, by an on-off valve that opens and closes based on commands from a control unit 50, which will be described later.

[0046] The compression stage 12 is provided with a discharge passage 48 that discharges nitrogen gas from the insulation space 28. The discharge passage 48 has a discharge pipe 48a fixed to the outer tubular member 26 so as to open into the insulation space 28, and a discharge valve 48b that is a valve disposed on the discharge pipe 48a. The discharge pipe 48a may be open to the atmosphere, or may be connected to a tank (not shown) whose internal pressure is approximately atmospheric pressure. The discharge pipe 48a also functions as a pressure equalization means that makes the insulation space 28 approximately equal to atmospheric pressure. The leakage portion 29 is also part of the pressure equalization means.

[0047] The discharge valve 48b is configured, for example, by an on-off valve that opens and closes based on commands from the control unit 50 (described later). The discharge valve 48b may be omitted.

[0048] The compression stage 12 includes a hydrogen gas supply unit 59 that supplies hydrogen gas to the first space 37a in the adapter part 37, and a nitrogen supply unit 60 that supplies nitrogen gas to the second space 37b in the adapter part 37.

[0049] The hydrogen gas supply unit 59 has a hydrogen flow path 59a connected to a hydrogen gas source 61. The hydrogen gas source 61 contains hydrogen gas at room temperature. The hydrogen flow path 59a is connected to an outer peripheral wall that forms the first space 37a in the adapter unit 37. The hydrogen gas supply unit 59 supplies hydrogen gas from the hydrogen gas source 61 to the first space 37a in the adapter unit 37 through the hydrogen flow path 59a. For this reason, it can be said that the temperature of the hydrogen gas in the first space 37a is higher than the liquefaction temperature of the nitrogen gas in the second space 37b.

[0050] The nitrogen supply unit 60 has a nitrogen flow path 60a connected to a nitrogen gas source 62. The nitrogen flow path 60a is connected to an outer peripheral wall that forms the second space 37b in the adapter unit 37. The nitrogen supply unit 60 supplies nitrogen gas from the nitrogen gas source 62 to the second space 37b in the adapter unit 37 through the nitrogen flow path 60a. The nitrogen gas source 62 contains nitrogen gas at room temperature.

[0051] The hydrogen flow path 59a of the hydrogen gas supply unit 59 is provided with a hydrogen valve 59b, which is a valve that adjusts the pressure of the hydrogen gas flowing through the hydrogen flow path 59a, and the nitrogen flow path 60a is provided with a nitrogen valve 60b, which is a valve that adjusts the pressure of the nitrogen gas flowing through the nitrogen flow path 60a.

[0052] The hydrogen gas in the first space 37a and the nitrogen gas in the second space 37b are discharged to the vent 70. The hydrogen gas in the first space 37a and the nitrogen gas in the second space 37b may be collected in a predetermined tank or returned to the hydrogen gas source 61 and the nitrogen gas source 62, respectively.

[0053] The supply valve 46b and the discharge valve 48b are communicatively connected to the control unit 50. The control unit 50 controls the supply valve 46b and the discharge valve 48b so that the supply valve 46b and the discharge valve 48b open when the piston 32 is driven by the crank mechanism 14, and close when the piston 32 is stopped. In other words, the control unit 50 controls the supply valve 46b and the discharge valve 48b to open based on a signal for driving the crank mechanism 14.

[0054] The hydrogen valve 59b and the nitrogen valve 60b are also communicatively connected to the control unit 50. The control unit 50 controls the hydrogen valve 59b and the nitrogen valve 60b so that the hydrogen valve 59b and the nitrogen valve 60b open when the piston 32 is driven, and close when the piston 32 is stopped.

[0055] Here, we will explain the operation of the compressor unit 10. In the compressor unit 10, when the crank mechanism 14 is operated, the piston 32 is operated, and hydrogen gas, which is boil-off gas, is drawn into the compression chamber 34 from the suction passage 21, and the hydrogen gas is compressed.

[0056] While the crank mechanism 14 is driven, the supply valve 46b, the exhaust valve 48b, the hydrogen valve 59b, and the nitrogen valve 60b are open. Therefore, while the piston 32 is moving, nitrogen gas is constantly or intermittently supplied from the nitrogen gas supply unit 46 to the insulation space 28. The nitrogen gas in the insulation space 28 is mainly released into the atmosphere through the exhaust passage 48, and is also released into the atmosphere through the leaking portion 29. In this way, while the compression stage 12 is compressing the hydrogen gas, nitrogen gas continues to flow through the insulation space 28, so that the oxygen gas that was around the cylinder portion 31 before the compressor was driven is discharged and prevented from liquefying. Furthermore, the nitrogen gas is cooled and prevented from liquefying.

[0057] Furthermore, while the crank mechanism 14 is being driven, the hydrogen gas supply unit 59 supplies hydrogen gas to the first space 37a in the adapter part 37, and the nitrogen supply unit 60 supplies nitrogen gas to the second space 37b in the adapter part 37. This prevents the nitrogen gas in the second space 37b from mixing with the hydrogen gas in the compression chamber 34 through the rod packing part 36.

[0058] As described above, in this embodiment, nitrogen gas is filled into the heat insulating space 28 between the cover part 25 and the cylinder part 31, so that the oxygen concentration of the air can be reduced as much as possible within the heat insulating space 28. This prevents the air (outside air) around the cylinder part 31 from being cooled by the boil-off gas (intake gas) of liquefied hydrogen, which is a low-temperature gas, and therefore prevents oxygen, which is a combustion-supporting gas, from being liquefied.

[0059] While the compression stage 12 is compressing the hydrogen gas, nitrogen gas continues to be discharged from the insulating space 28 through the various nitrogen gas discharge sections, namely the discharge passage section 48 and the leakage section 29, thereby preventing the nitrogen gas from being cooled and liquefied.

[0060] Furthermore, the nitrogen gas exhaust section also functions as a pressure equalization means, thereby equalizing the pressure inside and outside the insulation space 28. This improves maintainability compared to a configuration in which the insulation space 28 is maintained in a vacuum state. In other words, since the insulation space 28 does not need to be evacuated, there is no need to install equipment to evacuate the insulation space 28. Furthermore, the plate material for the outer tubular member 26 does not need to be thick enough to withstand the pressure difference. The openings in the outer tubular member 26 do not need to be provided with multiple bolts to contain the pressure. Because no sealing function is required, weight can be reduced and simplified structures such as bolts and seals can be used. This improves maintainability and makes it easier to accommodate larger sizes.

[0061] In this embodiment, the adapter 37 is provided with the partition 44, which more reliably prevents contact between the low-temperature boil-off gas (suction gas) and the nitrogen gas. The temperature of the hydrogen gas in the first space 37a, which is the space on the compression chamber 34 side, is higher than the liquefaction temperature of the nitrogen gas in the second space 37b, which is the space on the crank mechanism 14 side, so that liquefaction of the nitrogen gas can be prevented.

[0062] In this embodiment, the compression stage 12 may be horizontal. In this case, if the lower side is the suction side, the support portion of the cylinder portion 31 is provided on the suction side, which has a lower temperature, which may increase the effects of freezing and thermal contraction around the support portion. Furthermore, even if nitrogen liquefies on the outer surface of the cylinder portion 31, the liquid is gasified by flowing to the lower, higher-temperature discharge side. In contrast, if the suction valve 21a is configured to be located on the upper side in the direction of gravity, the support portion is provided on the discharge side, which has a higher temperature, which may reduce the effects of freezing and thermal contraction.

[0063] In this embodiment, the supply valve 46b is configured as an on-off valve, but is not limited to this and may be configured as an electric valve with an adjustable opening. In this case, as shown in Fig. 2, a temperature sensor 52 may be provided to detect the temperature of the nitrogen gas in the discharge pipe 48a of the discharge passage 48 or the temperature of the nitrogen gas in the insulation space 28. When the temperature sensor 52 is provided to detect the temperature of the nitrogen gas in the insulation space 28, the temperature sensor 52 is preferably disposed near the suction passage 21 or the suction valve 21a so as to be able to detect the temperature of the nitrogen gas in the insulation space 28 near the suction passage 21 or the suction valve 21a.

[0064] The control unit 50 may be configured to change the opening degree of the supply valve 46b based on the temperature detected by the temperature sensor 52. Specifically, when the temperature detected by the temperature sensor 52 is equal to or lower than a threshold value estimated from the liquefaction temperature of nitrogen gas (i.e., set based on the liquefaction temperature of nitrogen gas), the control unit 50 controls the supply valve 46b to increase the amount of nitrogen gas supplied to the insulation space 28. In other words, when liquefaction of the nitrogen gas in the discharge pipe 48a or the nitrogen gas in the insulation space 28 is likely to occur, a larger flow rate of nitrogen gas is supplied to the insulation space 28. This makes it possible to prevent liquefaction of the nitrogen gas.

[0065] In this embodiment, as shown in Fig. 1, one partition 44 is provided in the adapter part 37, but this is not limited to this. As shown in Fig. 3, two partitions 44 may be provided, or more partitions 44 may be provided.

[0066] In this embodiment, if nitrogen gas is sufficiently discharged through the discharge passage 48, there is no need to actively provide the leak portion 29. Furthermore, by adjusting the size and number of the leak portion 29, it is possible to have it function as a nitrogen gas leak portion and pressure equalization means, so it is also possible to omit the discharge passage 48.

[0067] (Second embodiment) In the first embodiment, the cover portion 25 is configured with an outer cylinder member 26 made of a material that does not easily deform, whereas in the second embodiment, as shown in Fig. 4, the cover portion 25 is configured with a sheet member 74 that covers a heat insulating material 72 attached to the cylinder portion 31. Note that the same components as in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0068] In the second embodiment, a heat insulating material 72 is provided so as to cover the cylinder portion 31. The heat insulating material 72 can be wrapped around the cylinder portion 31 as desired. The heat insulating material 72 is a cotton-like or sponge-like material such as glass wool, and is arranged so as to cover the entire outer surface of the cylinder portion 31, thereby making it difficult for heat from the outside air to be transmitted to the cylinder portion 31. The heat insulating material 72 is wrapped around the cylinder portion 31 and fixed with a band (not shown). It is also possible to use a pre-formed material, or a combination of these.

[0069] The sheet member 74 covering the heat insulating material 72 is made of a material that is lighter and softer than the outer cylinder member 26, which is made of metal or the like. In other words, the sheet member 74 only needs to have the function of preventing the heat insulating material 72 from being exposed to the outside, and does not need to be a rigid member that can form a space of a predetermined size by itself.

[0070] A moisture-proof sheet 75 may be provided inside the heat insulating material 72. That is, the moisture-proof sheet 75 may be wrapped around the outer surface of the cylinder portion 31, and the heat insulating material 72 may be provided to cover this moisture-proof sheet 75. Alternatively, a moisture-proof sheet 75 may be provided on this heat insulating material 72, and another heat insulating material 72 may be provided on the outside of that. In this case, the sheet member 74 is provided to cover the outer heat insulating material 72. That is, the moisture-proof sheet 75 and the heat insulating material 72 may have a multi-layer structure.

[0071] In the second embodiment, nitrogen gas is supplied to the space inside the sheet member 74, and a heat insulating material 72 is disposed in this space. Therefore, the space inside the sheet member 74 functions as a heat insulating space 28 for thermally insulating the cylinder portion 31 from the outside air.

[0072] The sheet member 74 is waterproof. Furthermore, the sheet member 74 may be breathable so that the nitrogen gas in the heat insulating space 28 can be discharged.

[0073] The sheet member 74 is provided with openings through which the piping forming the discharge flow path 18 passes, and also with openings through which the piping forming the suction flow path 21 passes. Leakage portions 29 (i.e., holes or gaps) are intentionally provided between these piping and the openings. Note that the sheet member 74 may also have additional leakage portions at locations other than the openings.

[0074] In the compressor unit 10, while the compression stage is compressing hydrogen gas, nitrogen gas is supplied from the nitrogen gas supply unit 46 to the insulation space 28 constantly or intermittently. The nitrogen gas in the insulation space 28 is released into the atmosphere through the leaking portion 29. Furthermore, because the sheet member 74 is breathable, the nitrogen gas can be discharged from the entire sheet member 74 (i.e., the sheet member 74 itself functions as a nitrogen gas discharge portion). In this way, by allowing the nitrogen gas to continue flowing through the insulation space 28, the oxygen gas that was around the cylinder portion 31 before the compressor was driven is discharged and prevented from liquefying. Furthermore, the nitrogen gas is cooled and prevented from liquefying.

[0075] In the compressor unit 10, by adjusting the size and number of the leakage parts 29 and by using a highly breathable sheet member 74, the leakage parts 29 and the sheet member 74 themselves can function not only as nitrogen gas leakage parts, but also as pressure equalization means that make the insulation space 28 approximately equal to atmospheric pressure.

[0076] In this embodiment, the cover 25 is configured with a sheet member 74 arranged to cover the insulating material 72. Therefore, compared to a case in which the cover 25 is configured with an outer tube member 26 fixed to the cylinder 31, the burden of attaching and detaching the cover 25 during maintenance can be reduced, and it is easier to accommodate larger cylinders with more complex shapes. In other words, compared to a case in which the cover 25 is configured with a metal outer tube member 26, the components constituting the cover 25 can be made lighter, improving maintainability. Furthermore, since the work of covering the insulating material 72 with the sheet member 74 can be done manually, the burden of the attachment and detachment work is reduced. This also reduces the burden of maintenance work on the cylinder 31. The sheet member 74 may be made of a non-breathable material as long as it can sufficiently discharge nitrogen gas through the leaking portion 29.

[0077] In this embodiment, as in the first embodiment, the supply valve 46b may be configured as an electrically operated valve with an adjustable opening. In this case, as shown in FIG. 5, a temperature sensor 52 may be provided to detect the temperature of the nitrogen gas in the discharge pipe 48a of the discharge passage 48 or the temperature of the nitrogen gas in the insulation space 28. The control unit 50 is configured to change the opening of the supply valve 46b based on the temperature detected by the temperature sensor 52. Specifically, when the temperature detected by the temperature sensor 52 is equal to or lower than a threshold value estimated from the liquefaction temperature of the nitrogen gas (i.e., set based on the liquefaction temperature of the nitrogen gas), the control unit 50 controls the supply valve 46b to increase the amount of nitrogen gas supplied to the insulation space 28. In other words, when liquefaction of the nitrogen gas in the discharge pipe 48a or the insulation space 28 is likely to occur, a larger flow rate of nitrogen gas is supplied to the insulation space 28. This prevents the nitrogen gas from liquefying.

[0078] Although a description of other configurations, operations, and effects will be omitted, the description of the first embodiment can be applied to the second embodiment. Furthermore, the present invention is not limited to the above-described embodiments, and various changes, modifications, etc. are possible without departing from the spirit of the present invention. [Explanation of symbols]

[0079] 10: Compressor unit 12: Compression stage 14: Crank mechanism 18a: Discharge valve 21: Suction passage 21a: Suction valve 23: Liquid hydrogen storage tank 25: Covering part 26: Outer cylinder member 28: Insulation space 31: Cylinder section 32: Piston 33: Piston rod 34: Compression chamber 37: Adapter part 44: Partition 46: Nitrogen gas supply unit 48: Discharge passage section 50: Control unit 52: Temperature sensor 72: Insulation material 74: Sheet material

Claims

1. A reciprocating compressor unit that recovers boil-off hydrogen gas from a liquid hydrogen storage tank and supplies at least a portion of the recovered hydrogen gas to a demand destination including at least one of an engine, a power generation facility, or a boiler, a compression stage that compresses hydrogen gas flowing out of the liquid hydrogen storage tank and through a suction passage; a crank mechanism that drives the compression stage; Equipped with The compression stage comprises: A cylinder portion; The piston and a cover portion disposed on the outside of the cylinder portion; a nitrogen gas supply unit that supplies nitrogen gas to the heat insulating space between the cover unit and the cylinder unit; a nitrogen gas discharge unit that discharges nitrogen gas from the heat insulating space while the compression stage is compressing the hydrogen gas; Equipped with The compressor unit comprises: The compressor unit further includes a control unit that controls the nitrogen gas supply unit so that nitrogen gas is supplied into the heat insulating space while the compression stage is compressing the hydrogen gas.

2. 2. The compressor unit according to claim 1, further comprising a pressure equalization means for making the pressure inside said heat insulating space approximately equal to atmospheric pressure.

3. 3. The compressor unit according to claim 1, wherein the cover portion is configured by a metallic outer cylindrical member fixed to the cylinder portion so as to maintain the formation of the heat insulating space in a predetermined shape.

4. The compressor unit according to claim 3, wherein the nitrogen gas discharge section comprises a discharge passage section having a discharge pipe fixed to the outer tubular member so as to open into the insulation space, and a discharge valve which is a valve disposed on the discharge pipe.

5. a temperature sensor for detecting the temperature of the nitrogen gas in the exhaust passage, The compressor unit according to claim 4, wherein the control unit controls the nitrogen gas supply unit so as to increase the amount of nitrogen gas supplied when the temperature detected by the temperature sensor is below a threshold value estimated from the liquefaction temperature of the nitrogen gas.

6. Further provided with a cotton-like or sponge-like insulating material, The cover portion is configured by a sheet member arranged to cover the heat insulating material, The compressor unit according to claim 1 or 2, wherein the nitrogen gas supply unit supplies nitrogen gas into the heat insulating space inside the sheet member.

7. The compressor unit according to claim 6 , wherein the cover portion is breathable.

8. Further provided is a temperature sensor for detecting the temperature of the nitrogen gas in the heat insulation space, The compressor unit according to claim 7, wherein the control unit controls the nitrogen gas supply unit so as to increase the amount of nitrogen gas supplied when the temperature detected by the temperature sensor is below a threshold value estimated from the liquefaction temperature of nitrogen gas.

9. the compression stage further includes an adapter portion that connects the cylinder portion and a case of the crank mechanism, the adapter portion includes at least one partition portion that divides an inner space of the adapter portion into a plurality of spaces; hydrogen gas is present in the space closest to the compression chamber among the plurality of spaces, and nitrogen gas is present in the space closest to the crank mechanism among the plurality of spaces, 3. The compressor unit according to claim 1, wherein the temperature of the hydrogen gas in the space closest to the compression chamber is higher than the liquefaction temperature of the nitrogen gas in the space closest to the crank mechanism.

10. the compression stage is a horizontal type in which the piston slides horizontally, The cylinder portion is a suction valve located on the upper side in the direction of gravity; a discharge valve located on the lower side in the direction of gravity; The compressor unit according to claim 1 or 2, comprising:

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